Permeability tuning system



Nov, 1, 1949 w. F. SANDS 2,486,986

PERMEABILITY TUNING SYSTEM Filed June 28, 1943 IN VEN TOR.

ATTORNEY Patented Nov. 1, 1949 PERMEABILITY TUNING SYSTEM William Francis Sands, West Collingswood, N. J., assignor` to Radio Corporation of America, a

corporation of Delaware Application June 28, 1943, Serial No. 492,506

12 Claims. 1

My present invention relates to a variable permeability tuning system for superheterodyne receivers, and more particularly to means employed in a tuning system of the type mentioned for effecting tracking between the signal frequency and oscillator circuits of such receivers over a predetermined tuning range.

In receivers of the superheterodyne type it is essential for satisfactory operation that the resonant frequency of the signal or antenna circuit differ from that of the oscillator circuit by substantially a constant amount, this difference frequency being commonly known as the intermediate frequency. It is the usual practice in such receivers to tune the oscillator circuit through a frequency range higher than the range through which the signal circuit is tuned. As a result, in order to insure a constant frequency difference, the frequency range of the oscillator circuit must be narrower, and if the variable tuning elements of the two circuits are to be uni-controlled, as is the usual practice, suitable means must -be provided whereby the frequency variation of the oscillator circuit is slowed up so that it can keep in step with the frequency variation of the signal circuit.

It is therefore one of the objects of my invention to provide, in a superheterodyne radio receiver, an improved variable permeability tuning system for causing the oscillator and signal input circuits to track accurately one with the other at a multiplicity of points `throughout a predetermined frequency range.

There are several known methods and means for effecting tracking in the tuning of two or more circuits by variable permeability tuning means, some of which are impracticable because of cost or manufacturing diiculties. One method of securing tracking in a permeability-tuned superheterodyne receiver for the broadcast band uses a variable-pitch winding for the oscillator inductor. Another method is disclosed and claimed in the patent to V. D. Landon, No. 2,248,242, assigned to the same assignee as the present application, and involves the use of a larger diameter winding for the oscillator inductor than for the signal frequency inductor and the connection of an adjustable capacitor across a lesser portion of the oscillator inductor, the associated tuning core entering the shunted portion of the inductor. The lesser portion is substantially one-third the length, from the core entering end to the tap on the winding.

A further method is disclosed and claimed in the patent to W. H. Conron, No.` 2,263,613, as-

signed to the same assignee as the present application, and involves the use of an oscillator inductor of larger winding diameter than that of the signal frequency inductor and the connection of an adjustable inductor in parallel across the whole of the oscillator` inductor, 1 t.

(Cl. Z50-20) The system according to the present invention embodies an alternative arrangement and utilizes one or more adjustable tracking inductors shunted across one or more lesser portions, respectively of the oscillator tuning inductor winding, said one or more portions being removed from the low radio frequency (R. F.) potential end thereof, or a combination of an adjustable tracking inductor and an adjustable tracking capacitor shunted across lesser portions of the oscillator inductor 'winding at the high and low potential ends thereof, respectively, or an adjustable tracking inductor shunted across a lesser portion of the signal frequency tuning inductor winding at the low patential end thereof. 'I'he term lesser is employed to designate a portion less than half the length of the winding.

The novel features characteristic of my invention are set forth with particularly in the appended claims. The invention itself, however, both as to its organization and mode of operation together with further objects and advantages thereof, will best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 illustrates a typical circuit of a tuning system for a superheterodyne receiver in which there has been embodied the present invention,

Figs. 2, 3, 6 and 7 show modified forms of the invention disclosed in Fig. 1, and

Figs. 4 and 5 show alternative mountings for certain circuit elements shown diagrammatically in certain other gures.

Referring rst to Fig. 1 which illustrates one form of the invention as applied to a typical converter circuit of a superheterodyne receiver, the tunable signal input circuit is shown at I and the tunable oscillator circuit at 2. In the signal input circuit, the variable tuning inductor comprises a iirst solenoid winding Ls provided with a first movable tuning core indicated at Cs, while in the oscillator or second circuit, the tuning inductor comprises a second solenoid winding L0 provided with a second movable tuning core C@ mechanically connected with the rst tuning core, as indicated by the dotted line 3, for unitary tuning control movement.

' The circuit i includes a shunt fixed capacitor 4 for the inductor LSCS and a shunt trimmer capacitor 5, the latter being adjusted to establish the low frequency end of the tuning range when the core CS is moved fully within the winding Ls. The circuit I is connected to ground as indicated vat t and is connected at its high potential side to 'any suitable signal source, such as an antenna 1,

`LC comprising twoseries connected capacitors H9' and lil, the latter being adjustable in a similar manner to the capacitor 5, for adjusting the alignment at the low frequency end of the tuning range of the circuit 2. The oscillator circuit in the present example is of the Colpitts type, having a cathode connection II between the capacitors 9 and III, and being grounded as indicated at I2, at the low potential side thereof.

The input circuit I is connected at its high potential side to a signal input grid I3 of a combined detector-oscillator tube I4. The cathode I5 is connected to ground I6 through a suitable radio frequency choke coil I1, the cathode terminal I8 of which is connected with the cathode tap II of the oscillator circuit.

The circuit 2 is connected with a second signal grid I 9 in the tube I4 for electronically mixing the signals from the circuit I with the locally generated oscillations to produce a fixed predetermined intermediate frequency in the output anode circuit 2U of the detector-oscillator tube. Feedback for the production of oscillations is provided in connection with the screen grid 2|, which functions as an anode connected to ground through a by-pass capacitor 22. A filter resistor 23 is connected between the screen grid and its supply source indicated at 24. The oscillator grid is provided with the usual grid coupling capacitor 25 and grid leak 26 to ground.

The high potential end of circuit I is connected to signal input grid I3 through a coupling capacitor 21 and the grid resistor 28 is connected to a bias supply lead 2'9, the junction therebetween being connected to ground through a bypass capacitor 3Q. Signals are derived from the output circuit 2D of the detector-oscillator system through a suitably tuned intermediate frequency coupling transformer 3|.

In permeability tuned superheterodyne circuits such as described above, it is customary to provide uniformly wound tuning inductors of the solenoid type, and to secure the required tracking at the two extreme ends of the band (or at two arbitrarily chosen frequencies close to the ends of the band) by the use of an oscillator inductor winding (L0) of larger diameter than the signal frequency inductor winding (Ls) as in the above mentioned Landon and Conron patents. Two point tracking is also obtainable with the use of equal diameter inductor windings Ls and Le. In this case cores Cs and C0 may be of uniform diameter but differing permeabilities in the signal frequency and the oscillator circuits, respectively, or of uniform and substantially identical permeability but with the oscillator core C0 of a different diameter than the signal frequency core (Cs) or cores if there are more than one signal frequency circuit.

For satisfactory operation, however, it is necessary to produce a third or inner tracking point, and additional tracking points if desired. If by way of illustration only, it be assumed that a given oscillator frequency (fo) is higher than the corresponding signal frequency (fs) by the amount or value of the intermediate frequency (I. FJ, (i. e., f0=fs-II. F.), the desired third and additional cross-over points may be secured by any suitable means which will cause the inductance (or more correctly, the reactance) to vary most rapidly as the core is moved through the region of the end of the inductor winding which is first penetrated by the core, and to have the slowest change at the fully penetrated end of the inductor winding. The desired relationship for the variation in the inductance (or the reactance) of the oscillator inductor structure depends, of course, upon the intermediate frequency, the signal and the oscillator frequencies at the ends of the respective signal and oscillator range, and the particular geometry and structure of the signal frequency and oscillator inductor windings and cores.

In the-above mentioned Landon patent the desired third alignment, or cross-over point, is secured by shunting a low R. F. potential portion of the oscillator inductor winding with an adjustable tracking or trimmer capacitor. Since the resonant frequency of the tapped winding portion of the oscillator inductor and the shunt trimmer is considerably above the oscillator frequency, this region of the inductor is responsible for a morerapid'inductance change, i. e., the region behaves as though the density of winding of the inductor` had been physically increased in the tapped portion. In the above Conron patent in which a larger diameter oscillator inductor windingis used to secure the two end (or outer) tracking frequencies, an adjustable inductor is shunted across the entire oscillator inductor to determine the shape of the tuning curve.

I have determined that a third and intermediate or inner tracking point may be secured by placing an adjustable tracking inductor L1 across a lesser portion of the oscillator inductor winding, which portion is removed from the grounded end into'which the core enters and is connected between spaced points or taps 31 and 38 on the winding, as shown in Fig. l. Additional crossover or tracking points may be secured by adding additional taps andv shunt or parallel inductors as shown in Figures 2 and 3 which are partial views representing modifications of the oscillator portion shown to the right of the dash line :v-y in Fig. 1.

In Fig. 2` an additional shunt tracking inductor L2 is connected across an intermediate lesser portion of and to taps or points 38 and 4I] on the oscillator inductor winding L0 and is in series with the rst tracking inductor L1. In Fig. 3 an additional inductor L3 is shunted across a greater tapped portion of the inductor winding Lo, being connected to taps 31 and 42. Inductor L3 is partially in shunt across or in overlapping relation with the rst tracking inductor L1, or in shunt with the latter and an intermediate portion of the inductor winding L0 in series. The term greater tapped portion is intended to mean a portion that is greater than half the length of the winding. The inductors L1, L2 and L3 are shown adjustable as by means of movable iron cores, For a final design however the shunting inductors could be of a predetermined value and therefore non-adjustable. In Fig. 3 the tracking inductors L1 and L2 are connected in shunt with lesser and greaterlportions, respectively, of the oscillator tuning inductor winding L0.

In Fig. 4 a structure is shown in which a tracking inductor winding L4, corresponding to inductor L1 in Fig. 1, is wound on the oscillator winding form F somewhat removed from the oscillator tuning inductor Winding and connected to taps 31 and 38, as in Fig. 4. A tracking inductor may be wound over the tapped portion as at L5 in Fig. 5. Indeed, where the oscillator inductor winding is sufficiently widely spaced, it may be possible in some cases to wind the tracking inductor Ls between the turns of the tapped portion, and connected to taps 31 and 43, thus forming a bi-lar wound portionon the oscillator inductor. The species of Fig. 5 is part of the subject matter of 'patentV application Serial No.

29,628, filed May 27, 1948 for High-frequency strap-wound coils.

In the modification disclosed in Fig. 6 the shunting tracking inductor disclosed in Fig. 1 is combined with the shunting capa-citor arrangement utilized in the above Landon patent. The capacitor C1 is connected between tap 44 of winding L and ground, and with the tapped por-tion at the low potential end of the oscillator inductor provides one of the desired intermediate tracking points. The shunt tracking inductor L1 is connected between taps 31 and 38, and with the shunted portion at the high potential end `of the tuning inductor provides a further intermediate cross-over or tracking point.

If it is desired to have one end of the shunt tracking inductor at ground potential, the latter may be placed in the signal frequency circuit between tap 45 and ground, in shunt across a portion of the signal frequency inductor winding Ls, adjacent the end thereof which is at low R. F, potential and at which the core enters, as shown in Fig. 7. In this combination the tracking inductor functions similarly to the tracking inductor connected to the high potential end of the oscillator tuning inductor in Fig. 1. The core Cs is mechanically connected with core C0 of the untapped oscillator inductor winding L0 'as in Fig.

Specifically the present invention differs from the Landon and Conron arrangements in the following important respects. The Landon arrangement may be considered as a permeability tuning equivalent of the variable capacitor tuning arrangement in which the plates of the oscillator tuning condenser are differently shaped than those of the signal frequency circuits. It provides only a rst approximation to the continuously shaped oscillator plates case, and achieves the desired result by adding reactance changing means to the low potential or core entering end of the inductor winding. The Conron arrangement may be considered as a permeability tuning equivalent of the variable capacitor case using similar signal frequency and oscillator capacitors but with a shunt padding capacitor in the oscillator circuit, As previously stated, this arrangement is limited to two alignment points.

The present invention involves a diierent means than in the Landon arrangement of securing a permeability tuning equivalent of the cutplate capacitor case, it being possible with said means to procure an approximation to the continuously cut-plate equivalent, thereby resulting in a multiplicity of cross-over points. The desired result is achieved by reducing the reactance changing rate of the oscillator tuning inductor at the high R. F. potential end of the winding, or the portion of the winding which is removed from the core entering end. Stated somewhat differently, the shunt capacitor in the Landon arrangement increases the effective inductance of the tapped portion of the tuning inductor, whereas the shunt tracking inductor or inductors in the present invention decrease the effective inductance of the tapped or shunted portion or portions of the tuning inductor, and the tuning range thereof. This is a desirabletracking feature for the oscillator when tuned above the frequency of the signal circuit as in the illustration given above.

It is to be understood of course that the present invention for obtaining one or more intermediate tracking points may be used in conjunction with any of the known arrangements of the prior art 6 which provide two outer point tracking at 'or near the ends of the tuning range. Some of these are indicated in the legend applied to Fig. 1 of the drawing. One method involves the use of a larger inner diameter inductor winding for the oscillator than for the signal frequency circuits, the cores being of like diameter. A second method involves the use of similar diameter tuning inductor windings for both the signal frequency and oscillator circuits. The cores for the respective tuning inductors may be of identical geometry and of uniform but different permeability. Thus, for the generally employed use of the oscillator frequency above the signal frequency (i. e., f0=fs{-I. F.) the required shortening of the oscillator range may be secured by the use of a lower permeability for the oscillator core than for the signal core. Another method involves the use of similar diameter inductor windings as in the above second method, and in which the signal frequency and oscillator cores may each be of uniform diameter and permeability, and of the same permeability as each other, but the required shortening of the oscillator range may be secured by making the oscillator core of smaller diameter or cross-sectional area than that of the signal frequency core. In other words, in the iirst and third methods the effective radial spacing between the oscillator inductor winding and its core is greater than that between the signal frequency inductor winding and its core. Stated differently, the ratio of the effective diameter of the oscillator winding to that of its core is larger than the ratio of the effective diameter of the signal frequency Winding to that of its core.

While I have shown and described certain preferred embodiments of my invention, it will be understood that various modificati-ons and changes will occur to those skilled in the art without departing from the spirit and scope cf this invention. I therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim is:

1. In a variable permeability tuning system, the combination of a plurality of tunable signalconveying circuits and means in one of said circuits for effecting a predetermined tracking relation, with two outer tracking points and at least one inner tracking point, in the tuning of said circuit with at least one other of said circuits, said means comprising a tuning inductor winding of the solenoid type, an adjustable tracking inductor connected in shunt across a lesser portion of and to spaced points on said tuning inductor winding for eifecting said inner tracking point, and a movable tuning core of ferro-magnetic material movable within the inductor winding to vary the tuning thereof.

2. In a variable permeability tuning system, the combination of a plurality of tunable signalconveying circuits and means in one of said circuits for effecting a predetermined tracking relation, with two outer tracking points and at least one inner tracking point, in the tuning of said circuit with at least one other of said circuits, said means comprising a tuning -inductor winding of the solenoid type, a tracking inductor connected in shunt across a lesser portion adjacent to one end of said winding for effecting said inner tracking point and a tuning core of ferromagnetic material movable within and adapted to enter said winding at the end remote fromthe shunted portion thereof.

3. In a variable permeability tuning system, the combination of a plurality of tunable circuits and means in one of said circuits for effecting a predetermined tracking relation in the tuning of said circuit with at least one other of said circuits, said means comprising a tuning inductor winding of the solenoid type, a plurality of tracking inductors connected in shunt across different portions of said winding removed from one end thereof and a movable tuning core of comminuted ferro-magnetic material movable within and adapted to enter the winding at said end thereof.

4. In a radio tuning system, the combination of two tunable circuits each having a tuning inductor comprising a winding provided with a magnetic tuning core adapted to enter one end thereof and to move therethrough, thereby to provide variable tuning of said circuits over different frequency ranges, uni-control means for moving said cores conjointly in predetermined relation to each other, thereby to cause tracking in the tuning of said circuits, and a tracking inductor connected in shunt with a lesser portion of one of said windings to improve the tracking of said circuits in a predetermined portion of the tuning range of said system, said tracking inductor being of such a value as to substantially reduce the effective inductance of said lesser portion and the tuning range of said one of said tuning inductors.

5. In a superheterodyne receiver, the combination with a tunable signal circuit having a tuning inductor comprising a solenoid winding provided with a movable magnetic core tuning element, of an oscillator circuit having a second tuning inductor comprising a second solenoid winding and a second movable magnetic core tuning element adapted to enter one end thereof in the tuning movement of the core element, and means including an adjustable tracking inductor connected in shunt with a portion of one of said tuning inductor windings and to an intermediate tap thereon, said tracking inductor being of such value as to substantially reduce the eiective inductance of said portion and the tuning range of said one of said inductors.

6. The combination defined in claim wherein the inner surfaces of the solenoid windings and the magnetic cores are respectively of the same diameter and said one of said tuning inductors is said oscillator circuit inductor 7. The combination dened in claim 5 wherein the effective radial spacing between said winding and core of said oscillator tuning inductor is greater than that between said winding and core of said signal frequency inductor.

8. In a superheterodyne receiver, the combination with a tunable signal circuit comprising a tuning inductor having a solenoid winding provided with a movable magnetic core tuning element, of an oscillator circuit comprising a second tuning inductor having a second solenoid winding provided with a second movable magnetic core tuning element adapted to enter one end thereof in the tuning movement of the core element, and a tracking inductor connected in shunt with said second tuning inductor and between points thereon defining a lesser portion of the second tuning inductor at the end removed from the core-entering end for reducing the elective inductance of said portion and the tuning range of said second inductor, said oscillator circuit being tunable in unison with, and to a higher `frequency range than, said signal circuit.

9. In a superheterodyne receiver, the combination with a tunable signal circuit having a first tuning inductor comprising a rst solenoid winding provided with a rst movable magnetic core tuning element, of an oscillator circuit having a second tuning inductor comprising a second solenoid winding and a second movable magnetic core tuning element adapted to enter one end of the said second winding in the tuning movement of the core element, and a pair of inductors each connected in shunt with a different portion of and to an intermediate tap on the second winding at the end remote from the core-entering end.

10. The combination defined in claim 9 wherein the shunting inductors are connected in series with each other.

11. In a superheterodyne receiver, the combination with a tunable signal circuit having 'a first tuning inductor comprising a first solenoid winding provided with a rst movable magnetic core tuning element, of an oscillator circuit having a second tuning inductor comprising a second solenoid winding and a second movable magnetic core tuning element for said last `named winding adapted to enter one end thereof in the tuning movement of the second core element, a capacitor connected in shunt with a portion of and to an intermediate point on the second winding adjacent to said end, and a tracking inductor connected in shunt with a portion of and to an intermediate point on the second tuning inductor at the end remote from the core-entering end.

12. In a superheterodyne receiver, the combination with a tunable signal circuit having a first tuning inductor comprising a first solenoid winding provided with a rst movable magnetic core tuning element, of an oscillator circuit having a second tuning inductor comprising a second solenoid winding provided with a second movable magnetic core tuning element, said cores f adapted conjointly to enter corresponding ends of the said windings in the conjoint tuning movement of said cores, and a tracking inductor connected in shunt with a lesser portion of and to an intermediate point on the rst winding adjacent to the core-entering end thereof.

WILLIAM FRANCIS SANDS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,947,229 Runge Feb. 13, 1934 2,034,773 Roberts Mar. 24, 1936 2,095,035 Posthumus et al. Oct. 5, 1937 2,131,976 Schaper Oct. 4, 1938 2,149,336 `Darnell Mar. 7, 1939 2,190,048 Sinninger Feb. 13, 1940 2,222,387 Wheeler et al. Nov. 19, 1940 2,248,242 Landon July 8, 1941 2,263,613 Conron Nov. 25, 1941 2,310,323 Sharp Feb. 9, 1943 2,322,722 Wentworth June 22, 1943 2,359,684 Sands Oct. 3, 1944 2,383,286 Beers Aug. 21, 1945 FOREIGN PATENTS Number Country Date 477,104 Great Britain May 12, 1936 666,632 Germany Oct. 24, 1938 

